1. Field of the Invention
The present invention relates generally to input devices and, more particularly, to improvements for touch panel displays.
2. Background of the Related Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Input devices perform the function of providing some means for entering commands and data into a computer, data processor, or information system. A variety of input devices are currently available, including keyboards, light pens, data tablets, mice, track balls, joysticks, scanners, voice recognition devices, and touch screens. Each of these input devices exhibits various advantages and disadvantages, and the input device or devices used in any particular application are typically chosen to maximize the efficient input of information into the system.
This disclosure is primarily directed to the last of the input devices mentioned above, namely touch screens. Unlike the other input devices mentioned above, touch screens not only act as a data input device, they also act as a display unit. Essentially, a touch screen is a display unit with some form of a touch-sensitive surface. Due to this unique characteristic, touch screens are currently utilized in a variety of different applications, such as computer terminals, cash registers, automatic teller machines, and automated gasoline pumps to name just a few.
Currently, there are at least four different technologies used for touch screens: (1) capacitive; (2) resistive, (3) surface acoustic wave, and (4) light beam interruption. Although each of these different types of touch screens operate in a different manner and exhibit certain advantages and disadvantages, certain similarities exist. For example, regardless of the type of touch screen, the touch screen system typically includes a sensor unit, which senses the location touched on the display, and a controller unit, which interfaces with the sensor unit and communicates the location information to a system computer. Thus, regardless of the technology employed, each type of touch screen performs the same general function.
However, it is the differences in the way that the various types of touch screens operate that causes a designer to use one type of touch screen over another for a particular application. Resistive touch screens, for example, advantageously exhibit low cost, high touch point density, and can be operated with a gloved hand. Disadvantageously, however, resistive touch screens can be easily damaged and exhibit poor display characteristics (particularly in sunlight). Capacitive touch screens also provide high touch point density and low cost, but capacitive touch screens can be easily damaged, must be calibrated due to large temperature changes, and cannot be operated with a gloved hand.
In contrast, surface acoustic wave touch screens have no overlay to be damaged or to reduce the visual quality of the display. However, surface acoustic wave touch screens typically exhibit the highest cost and can be falsely triggered by noise, wind, transmission signals, and insects. Touch screens that use light beam interruption, typically called infrared touch screens, are relatively expensive. Advantageously however, they have no touch sensitive overlay to be damaged, exhibit high touch point density, can be operated with heavy gloves, exhibit good immunity to most false trigger sources, and are extremely rugged and weather sealable. Although these advantages typically make infrared touch screens the most suitable type of touch screen to use in outdoor applications, high ambient light conditions, such as direct sunlight, can cause an infrared touch screen to malfunction.
It can be seen that each type of touch screen exhibits some disadvantage which makes it not well suited for outdoor use, particularly in high ambient light conditions. Of the different types of touch screens mentioned above, resistive touch screens typically offer the lowest cost along with very good operational performance. In a resistive touch screen, a display, such as a liquid crystal display, resides beneath a multi-layered screen overlay. The top layer touched by a user is a plastic layer with a transparent metallic film on its underside. This top layer is separated by insulating spacers from a bottom layer that has a metallic film on its upper side. These metallic films face one another so that the films make contact when a user presses the top layer into contact with the bottom layer. A conductive path is formed at the point of contact. Thus, the films act as a voltage divider, and the voltage at the point of contact may be measured in the X and Y directions by applying the voltage in one direction and then the other direction. The measured voltages may then be sent to a controller where they are converted into coordinates on the screen and sent to a computer.
This overlay screen suffers in outdoor applications, and particularly in sunlight, for various reasons. First, the typical reflectance of such overlay screens is about 25%, making the underlying display difficult to read. Second, such overlay screens allow most of the infrared radiation from sunlight to be absorbed by the underlying liquid crystal display, and this radiation can cause solar thermal loading of the display which lead to display malfunction. Third, the materials used for such overlay screens tend to deteriorate rapidly from exposure to the ultraviolet rays of the sun. Fourth, the top layer touched by users is easily scratched or damaged, thus requiring the whole touch panel to be replaced.
The present invention may address one or more of the problems set forth above.